Silver halide emulsions for lithography



United States Patent US. Cl. 96-66.4 9 Claims ABSTRACT OF THE DISCLOSURE Photographic litho type silver halide emulsions containing an alkylated polymer of a heterocyclic N-vinyl monomer of the lactam series in which the alkyl radical of said polymer contains from 2 to 2000 carbon atoms.

The present invention relates in general to photography and in particular to the manufacture and development of photographic silver halide emulsions beneficially adapted for use in connection with half-tone and line photographic reproductions.

Photographic emulsions employed for pictorial purposes by professional and amateur photographers are specifically designed to provide upon post-exposure, photographic development an image of the medium or low-contrast type. In contradistinction, it is imperative that photographic emulsions employed for use in half-tone and line reproduction in the photomechanical and lithographic field be capable of providing an image of exceedingly high contrast in order to negotiate the critical requirements imposed by the lithographic and photo-engraving industry.

The sensitometric characteristics of photographic emulsion products are conventionally defined in terms of graphic analysis which reflect the light response properties exhibited by a given film sample under certain predetermined and precisely controlled conditions of exposure and development. This is accomplished for example by exposing the film sample in a sensitometer and thereafter developing the thus-exposed film under controlled and standardized conditions. The resulting densities are measured and plotted on a graph against the corresponding exposure values. A line drawn through the locus of plots obtained in this manner is conventionally termed the characteristic curve, i.e., the H & D curve for the particular photographic film sample being investigated. As Will be readily appreciated, since the vast majority of photomechanical processes require a film of extremely high contrast, optimum results are obtainable solely under certain and specific conditions, namely, the exposed portions of the film sample must be of uniform and maximum density while the unexposed or underunexposed portions of the film must be completely clear, i.e.,substantially devoid of developed silver. Thus, the characteristic curve of an ideal graphic arts film would portray a rather abrupt exposure differential as between the minimum and maximum density regions. Otherwise stated, the slope of the H & D curve would be relatively steep.

However, many of the photographic emulsion materials promulgated in the art for use in graphic arts processing are found to be notably deficient as regards the provision of the requisite high contrast result. Perhaps the primary objection relates to the fact that the characteristic curve of such film materials possesses a relatively extended or protracted intermediate exposure range, i.e., the H & D curve displays a rather gradual exposure differential between minimum and maximum density regions giving rise to a shallow slope. Consequently, and unless precise and predetermined adjustments are made in connection with the exposure and development operations, the half-tone dot image obtainable with such films will invariably exhibit inferior contrast, definition, resolution, etc., such deleterious effects usually being manifested in the form of dot fuzziness.

The aforedescribed disadvantages become exceedingly pronounced in those instances wherein the film material in question is subjected to high speed processing, e.g., applications involving the use of automatic processing machines. As is commonly understood in the industry, the relatively recent and widespread emergence of automatic processing techniques and the industrial importance commanded thereby has correspondingly imposed upon the film manufacturer even more stringent requirements. Thus, the sensitometric properties of the film sample must remain undisturbed despite the rather extreme conditions of solution activity, temperature, concentrations, etc. incident to high speed, automatic film processing. Consequently, the film processors latitude of operations has been circumscribed significantly since the opportunity for the exercise of human judgment, e.g., inspection, observation, etc. is virtually non-existent. This situation has necessarily emphasized the importance of providing photographic films having constancy of sensitometric properties.

In an effort to overcome or otherwise mitigate any tendency of graphic arts film materials to exhibit fluctuations in sensitometric properties, considerable industrial activity has centered around the research and development of substances, e.g., emulsion additives, which exhibit emulsion stabilizing effects over a Wide range of operating parameters. For example, it is well known that the contrast and developability of silver halide emulsion materials can be augmented by incorporating therein condensation product of low molecular weight alkylene oxides such as for example homoand co-polymers of ethylene oxide. Methods for so proceeding are described extensively in the prior art both patent and otherwise.

Despite the meritorious improvements characterizing much of the industrial effort heretofore expended in this regard, the advantage to the film manufacturer has in many instances been marginal only. For example it has been ascertained that many of the emulsion additives tend to deleteriously affect other properties considered essential in the emulsion product, e.g., fog, stability upon standing exhaustion characteristics and image tone in the developed silver image. The latter mentioned aspect has proved to be a particular source of difiiculty in that the fugitive brown to reddish-brown tone of the toe silver gives rise to half-tones with undesirable appearance as well as reduced transparency to blue light in the areas surrounding the half-tone dots.

Thus, a primary object of the present invention resides in the provision of photographic silver halide emulsions specifically and beneficially adapted for use in connection with half-tone and line reproduction wherein the foregoing and related disadvantages are eliminated or at least mitigated to a substantial extent.

Another object of the present invention resides in the provision of photomechanical silver halide emulsions capable of providing a high contrast silver image having high contrast, image quality reduced fog, etc.

A further object of the present invention resides in the provision of photomechanical silver halide emulsion capable of providing a high contrast silver image having exceptionally clear background or non-image areas and wherein the silver image deposits are totally devoid of fugitive shifts in tone or coloration.

Other objects and advantages of the present invention will become more apparent hereinafter as the description proceeds.

The attainment of the foregoing and related objects is made possible in accordance with the present invention which in its broader aspects provides incorporating into a photographic silver halide emulsion of the photomechanical, i.e., lith type an alkylated polymer of a heterocyclic N-vinyl monomer of the lactam series in which the alkyl radical of said polymer contains from 2 to 2000 carbon atoms.

The alkylated, N-vinyl lactam polymers contemplated for use in practicing the present invention are those prepared by alkylation of a homopolymer or copolymer of a heterocyclic N-vinyl monomer, preferably a N-vinyl lactam monomer and most preferably N-vinyl pyrrolidone monomer with an alpha-olefin containing from 2 carbon atoms to 2000 carbon atoms preferably in the range of from 2 to 200 carbon atoms, and most preferably in the range of from 8 to 42 carbon atoms, said alkylation process being more fully described in General Aniline and Film Corporations copending patent application, Ser. No. 508,547, filed Nov. 18, 1965, now Pat. No. 3,417,054, or by simultaneously polymerizing and alkylating a mixture containing the N-vinyl lactam monomer, a monoethylenically unsaturated polymerizable monomer and an alpha-olefin containing from 2 carbon atoms to 2000 carbon atoms or a mixture of two different heterocyclic N- vinyl monomers and an alpha-olefin containing from 2 carbon atoms to 2000 carbon atoms, said simultaneous polymerization and alkylation process being more fully described in General Aniline and Film Corporations copending patent application, Ser. No. 525,374, filed Feb. 7, 1966, now Pat. No. 3,423,367.

As examples of N-vinyl lactam monomers which contain a carbonyl function adjacent to the nitrogen in the heterocyclic moiety, whose alkylated polymeric derivatives produced as described in said applications, Ser. Nos. 508,547 and 525,374, may be employed in practicing the present invention may be mentioned N-vinyl succinimide, N-vinyl diglycolylimide, N-vinyl glutarimide, N-vinyl-3- morpholinone, N-vinyl-5-methyl-3-morpholinone, N-vinyl- 5-ethyl-3-morpholinone, N-vinyl oxazolidone, etc., and N- vinyl ring oxygenated lactams as disclosed in US. Pat. 3,231,548, and especially the N-vinyl 5-,6- and 7-membered lactams, particularly N-vinyl pyrrolidone, characterized by the following formula:

| L CH GHQ-1m wherein R and R are selected from the group consisting of hydrogen, methyl and ethyl, n is an integer of from 1 to 3, and m represents the average molecular weight as determined by relative viscosity measurement which are designated as K values.

The viscosity coeificient K, which is fully described in Modern Plastics, vol. 23, No. 3, pp. 157-61, 212, 214, 216 and 216 (1945) is calculated as follows:

The homopolymers of the N-vinyl lactams characterized by the foregoing formula (whose alkylated derivatives obtained, for example, as described in said application Ser. No. 508,547 are suitable for use in practicing the present invention) are readily obtained by homopolymerizing N- vinyl pyrrolidone; N-vinyl-S-methyl pyrrolidone; N-vinyl- S-ethyl pyrrolidone; N-vinyl-5,5-dimethyl pyrrolidone; N- vinyl-5,5-diethyl pyrrolidone and N-vinyl-S-methyl-S-ethyl pyrrolidone; N-vinyl piperidone; N-vinyl-o-methyl piperidone; N-vinyl-6-ethyl piperidone; N-vinyl-6,6-dimethyl piperidone; N-vinyl-6,6-diethyl piperidone and N-vinyl-6-rrrethyl-6-ethyl piperidone; N-vinyl caprolactam, N-vinyl-7-methyl caprolactam; N-vinyl-7,7-dimethyl caprolactam; N-vinyl-7-ethyl caprolactam; N-vinyl-7,7- diethyl caprolactam and N-vinyl-7-methyl-7-ethyl caprolactam.

For the purpose of the present invention we employ alkylated derivatives of homopolymers of heterocyclic N-vinyl monomers having a K value ranging from about 10 to 140, preferably from about 30 to 100. These homopolymers are readily obtained by conventional homopolymerization procedures of the foregoing heterocyclic N-vinyl monomers described in US. Pats. 2,265,- 450; 2,317,804; 2,335,454 and many others too numerous to mention in which working examples are given.

All of the homopolymers of N-vinyl lactams characterized by the foregoing general formula are soluble in water, alcohols, and certain classes of organic solvents, but insoluble in the aliphatic and aromatic hydrocarbons of the type hereinbefore mentioned.

Copolymers obtained by copolymerizing 5 to 99 mole percent of the foregoing heterocyclic N-vinyl monomers with 1 to mole percent of a monoethylenically unsaturated polymerizable monomer and having a K value from about 10 to are readily alkylated in accordance with the present invention to yield products having solubility. characteristics dictated by the end use.

The various monoethylenically unsaturated polymerizable monomers, which are copolymerized with any one of the aforementioned heterocyclic N-vinyl monomers in the conventional manner and which will yield copolymers that are readily alkylated in accordance with said application Ser. No. 508,547, to produce alkylated copolymers suitable for use in practicing the present invention, including vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl lactate, vinyl caproate, vinyl caprylate, vinyl oleate, and vinyl stearate; acrylonitrile; vinyl ketones; vinyl cyclohexane; styrene; 2-vinyl pyridine; 4-vinyl pyridine; acrylic acid; acrylate ester monomers of the formula:

CHFCHCOOR wherein R represents either a straight or branched alkyl of from 1 to 18 carbon atoms or an alkoxyalkyl in which the total number of carbon atoms in the alkyl groups range from 3 to 6.

As examples of such acrylate esters the following are illustrative: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, Z-methyl-l-butyl, 3-methyl-l-butyl, 2- ethyl-l-butyl, amyl, 3-pentyl, 2-methyl-1-pentyl, 4-methyl- 2-pentyl, hexyl, 2-ethyl-hexyl, heptyl, 2-hepty1, octyl, 2- octyl, nonyl, 5-ethyl-2-nonyl, decyl, 2-methyl-7-ethyl-4- undecyl, dodecyl, tetradecyl, hexadecyl, octadecyl, 2- methoxyethyl, 2-ethoxyethyl and 2-butoxyethyl acrylates; methacrylic monomers such as methacrylic acid, methyl methacrylate, cyclohexyl methacrylate, isobutyl methacrylate, isoamyl methacrylate, fl-methoxy ethyl methacrylate and a-(o-chlorophenyl) ethyl methacrylate, 13- phenoxy-ethyl methacrylate, a-phenyl ethyl methacrylate, phenyl methacrylate, o-cresyl methacrylate, p-cyclohexylphenyl methacrylate, 2-nitro-2-methyl propyl methacrylate, diethylamino-ethylmethacrylate, ethylidene acetate methacrylate and glycidyl methacrylate, including esters of halo acrylic acids, such as methyl-2-chloroacrylate, ethyl-ot-chloro-acrylate, phenyl-ot-chloro-acrylate,

a-ethylacrylic acid; methacrylonitrile; N-alkyl and N-aryl substituted acrylamides such as N-methyl acrylamide, N- ethyl acrylamide, N-propyl acrylamide, N-n-butyl acrylamide, N-n-dodecyl acrylamide, N-n-octadecyl acrylamide, N,N-dimethyl acrylamide, N,N-diethyl acrylamide, N-N-di-n-butyl acrylamide, N N di isobutyl acrylamide, N-cyclohexyl acrylamide, N,N-dicyclohexyl acrylamide, N-phenyl acrylamide, N-p nitro phenyl acrylamide, N-a-naphthyl acrylamide, N fi naphthyl acrylamide, N methyl N phenyl acrylamide, N,N diphenyl acrylamide, N-benzyl acrylamide, N,N-di-benzyl acrylamide; and grafted monomers of the type disclosed in Us. Pats. 3,029,219; 3,035,009; 3,036,033 and the like.

A mixture consisting of from to 99 mole percent of any one of the foregoing heterocyclic N-vinyl monomers and from 1 to 95 mole percent of a different heterocyclic N-vinyl monomer, such as, for example, N-vinyl lactam with either N-vinyl succinimide, N-vinyl-3-morpholinone, and the like, may also be copolymerized and the resulting copolymer alkylated for use in the present invention.

It is to be noted that any copolymer containing not less than 5 mole percent of the heterocyclic N-vinyl monomer and which is soluble in the organic solvent is readily alkylated in accordance with the present invention. From numerous experiments connected with the present invention, it has been found that the configuration of the foregoing monoethylenically unsaturated monomers, and numerous others, is immaterial since they all copolymerize in the aforementioned proportions with the heterocyclic N-vinyl monomers and yield copolymers which are soluble in the organic solvent or mixture thereof and which are readily alkylated.

With regard to the u-olefins employed for producing the alkylated polymers used in practicing this invention, it is to be noted at the outset that any a-olefins having a molecular weight from about 28 to as high as about 28,000, may be employed as the alkylating agent for the alkylated polymers of the various heterocyclic N-vinyl monomers. As examples of such u-olefins, the following are illustrative: ethylene, propylene, l-butene, l-pentene, Z-ethyl-l-butene, Z-methyl-l-pentene, l-hexene, S-methyll-hexene, 2-methyl-1-pentene, 3-ethyl-1-pentene, l-heptene, l-octene, l-nonene, Z-ethyl-l-hexene, l-decene, 1- dodecene, l-tetradecene, l-hexadecene, l-heptadecene, 1- octadecene, l-nonadecene, l-eicosene, l-docosene, l-tetracosene, l-pentacosene and polybutenes of molecular weight of 400 to 2500 may be employed.

While linear u-olefins are preferred because of their commercial availability, numerous isomers of rat-olefins ranging from l-pentene to l-pentacosene as well as polybutenes may also be employed in the alkylation reaction. The only requirement in such case is that the isomer contain ethylenic unsaturation in the a position thereof.

Instead of employing any one of the foregoing individual u-olefins, a mixture of commercially available linear a-olefins produced by cracking petroleum wax or by polymerizing lower olefins may also be used as the alkylating agent. Alpha-olefins in the carbon range of from Cg-Cq; G r-C9; C9C11; CIT-C; and C15-C20 are commercially available and may be used. A mixture of a-OlGfiIlS containing from 65 to 75 percent of a-olefins of from C to C carbon atoms having an average molecular weight of 366 is also commercially available and such mixture is employed in the alkylation reaction.

The aforedescribed lactam polymers when incorporated into photomechanical type silver halide emulsion make possible the realization of synergistic improvement in such emulsion properties as developability, contrast and edge-gradient. Moreover, such improvements obtain despite the subjection of such emulsion materials to high speed automatic machine processing involving the employment of severe operating conditions of temperature, solution activity, etc. as mentioned previously. The term edge-gradient as used herein is descriptive of that portion of the characteristic or H &. D curve which defines that differential of exposure corresponding to minimum and maximum density regions. Thus, this portion of the H & D curve would be rather steep with respect to the emulsions described herein. Approximately stated, the threshold recording level of emulsions so characterized would correspond in practical terms to maximum density values. A further and significant advantage relates to the fact that such improvements are realized in the total absence of any tendency for silver image discoloration, i.e., undesired shifts in silver image coloration are completely avoided. The N-vinyl lactam polymers of the present invention are likewise advantageous in that their solubility as well as diifusibility characteristics in gelatin layers may be controlled in accordance with the requirements and objectives of the processor. The solubility characteristics of the N-vinyl lactam polymers are materially influenced, if not determined, by the nature of the a-olefin employed in deriving the polymer material. Thus by regulating the relative proportions of u-olefin and N-vinyl lactam as well as the carbon chain length of the u-olefin the processor is able to control the hydrophilic/lipophilic balance of the copolymer.

The solubility characteristics of the polymer material are vitally important in connection with suitability for photographic processing; for example, should the polymer material exhibit a pronounced tendency to diffuse or otherwise migrate from the emulsion layer, this property characterizing many of the polyalkylene oxides heretofore provided for similar purposes, undesired contamination of processing solutions is inevitable. Consequently, the accumulation of such diffusion productions contributes significantly to the exhaustion rate of the developer, i.e., severely curtails the efficacy of repetitive developer use. In view of the wide latitude of discretion available to the processor as regards the selection of a specific N-vinyl lactam polymer, undesired developer contamination can be readily avoided by correspondingly selecting a polymer material possessing negligible diffusing tendency.

The N-vinyl lactam polymers contemplated for use herein are readily available commercially from the General Aniline & Film Corporation under the trade designation Ganex. Such polymers may be water or alcohol soluble depending upon the aforementioned hydrophilic/ lipophilic balance. Such polymer materials may be incorporated into the silver halide emulsion at any suitable stage of emulsion preparation in the form of an aqueous, alcoholic or aqueous alcoholic solution. The concentration of lactam polymer employed] may vary over a relatively wide range; in general, it has been found that concentrations ranging from about 0.1 to about 10 grams per mole of silver halide and preferably from 0.5 to 5.0 grams per mole of silver halide are eminently suitable for the cast majority of commercial applications. The aforestated concentration ranges are critical only in that they assure the obtention of optimum results. However, it is recognized that the particular requirements of the processor may dictate the propriety of departing from such ranges.

The photomechanical silver halide emulsions contemplated for use in accordance with the present invention comprise in general the unsensitized, orthochromatic panchromatic high contrast emulsions. Emulsions of this type are prepared utilizing as the light-sensitive silver salt, silver chloride, silver chlorobromide, and/or silver chlorobromoiodide. Particularly preferred for use are the fine grain silver halide emulsions containing at least 50 mole percent chloride and less than 50 mole percent bromide. Small concentrations of iodide can be tolerated if the, total silver iodide content of the emulsion does not exceed 3.0 mole percent based on the amount of silver nitrate used in the preparation of the emulsion. When silver chlorobromide emulsions are used, the relative amount of halides generally ranges from 2 to 8 parts of chloride per part of bromide. The term high contrast as used herein connotes emulsion materials of the aforedescribed type having a gamma higher than 8.0. Photographic emulsions of this type are well known in the art being described in numerous publications.

The aforedescribed photomechanical silver halide emulsions are specifically adapted for post-exposure development operations involving the use of developer compositions of the so-called infectious type, i.e., those which contain in addition to hydroquinone as the sole developing agent, a mixture of formaldehyde and potassium metabisulfite or the reaction of a formaldehyde and sodium bisulfite as described in U.S. Pat. 2,313,523. The

infectious developers are normally capable of producing images possessing gamma values of approximately 7.0 and higher.

Lithographic developers of the aforedescribed type are further characterized in that the free sulfite ion concentration is maintained within exceedingly small although rigorously controlled limits. The predominant portion of the alkali sulfite contained in the developer solution is usually present in the form of a formaldehydebisulfite addition compound which functions as a sulfite buffer. Control of sulfite ion concentration is a matter of critical import since excess sulfite vitiates any possibility of infectious development action. Moreover, should the sulfite concentration fall below that prescribed, the developed emulsion product will invariably manifest an intolerably high fog level. In addition, lithographic developers are invariably maintained at a high pH.

It will be further understood of course that lithographic developers differ from the more conventional developer types in that development time critically affects the possibilities of obtaining maximum gamma images. Thus, any departures from optimum developer-contacting intervals will in most instances result in serious impairment of image quality, e.g., low gamma. In general, optimum gamma values may be realized by employing developercontacting intervals ranging from about 1 /2 minutes to about 4 /2 minutes.

The light-sensitive silver halide emulsions described herein may be applied to any of the support materials conventionally employed for such purposes in the fabrication of light-sensitive elements. Examples of suitable support materials include, without necessary limitations, glass, cellulose acetate, synthetic polymeric materials such as polystyrene, polycarbonate, polyesters, e.g., polyethylene terephthalate and the like.

The following examples are given for purposes of illustration only and are not to be considered as necessarily constituting a limitation on the present invention.

EXAMPLE I A washed, fine grain gelatino silver chloro bromide emulsion containing approximately 85 mole percent chloride is divided into equal portions and 2 gm. of Ganex V-904 per mole of silver is added to one portion in the form of a 2% aqueous solution. Conventional additives such as gelatin hardeners, sensitizing dyes, antifoggants, coating surfactants, chemical sensitizers and like photographic addenda are added in equal amounts to both portions and the emulsions coated on a suitable support in conjunction with an antiabrasion surface overcoat composed of gelatin, ,gelatin hardener, and coating surfactant and allowed to dry.

Dry samples of each coating are exposed through an intensity scale sensitometer and processed in a lith developer at 68 F. for 2, 3, and 4 minutes respectively. Characteristic curves are then plotted in the normal manner and the effective contrast determined by:

(l) Locating a point 0.1 above fog (first point).

(2) Locating a second point, 0.4 Log E, to the right of this point.

(3) Drawing a vertical line so that it intersects the curve at a third point. The slope of this line represents effective contrast, designated E.C., as defined by F. J. Drago 1 and is indicative of the contrast of a photographic material when the toe and shoulder, 38 well as the straight line portion of the curve is included. The EC. is useful in predicting the half-tone dot quality obtainable with a given material, i.e., the higher the BC. the better the dot quality.

Using this technique, in conjunction with a subjective judgment of dot quality arrived at by visual examination of the dot structure using a microscope, the film samples are rated for their ability to produce half-tone dot quality when exposed in contact with a conventional line per inch magenta half-tone screen. The results obtained are itemized in the following table.

TABLE I Grains copolymer Copolymer per mole Relative Dot Film Additive of silver Speed EC. Quality (a) None 1. 00 3.8 Poor. (b) Ganex V904 2. 0 1. 23 7. 4 Good. (0) Ganex V-804 2.0 1.16 8.0 Very good.

Each of the emulsion samples itemized in the above table is processed in the following manner; subsequent to exposure, each of such samples is immersed for the prescribed in-terval in the following lithographic developer composition described in the Ansco Graphic Arts Handbook, p. 38 (1958):

Water liters 2.0 Sodium sulfite, anhydrous grams 120.0 Paraformaldehyde do 30.0 Potassium metabisulfite do- 10.5 Boric acid (crystals) do 30.0 Hydroquinone do 90.0 Potassium bromide do 6.0

Water to make 4.0 liters.

EXAMPLE II In order to evaluate the influence of development time upon the speed and effective contrast characteristics, Example I is repeated, i.e., identical film samples identified as (a), (b) and (0) respectively are processed as described. The relative speed and effective contrast of each of the emulsion samples for development periods of 2, 3 and 4 minutes respectively are summarized in the following table.

TABLE II 2 Development 3 Development 4 Development Relative Relative Relative Film Speed E.C. Speed E.O Speed E.C.

EXAMPLE III Examples I and II are repeated except that a graft copolymer of poly (vinyl pyrrolidone) and butene-l, commercially available under the trade name Ganex V804 is employed in lieu of Ganex V-904. The graft copolymer material is added in the form of 2% 1:1 aqueousmethanolic solution in amounts suflicient to yield a concentration of 2 gms. per mole of emulsion silver. Each 1 l J. Drago. Proe. 8th Annu. Tech. Meeting Assoc. Graphic Arts, p. 167 (1956).

of the emulsion samples, following subjection to the processing described in Examples I and II, exhibits excellent effective contrast and dot quality with accompanying significant improvement in speed.

This invention has been described with respect to certain preferred embodiments and there will become obvious to persons skilled in the art other variations, modifications, and equivalents which are to be understood as coming within the scope of the present invention.

What is claimed is:

1. A light-sensitive silver halide emulsion of the type suitable for half-tone reproduction said silver halide being selected from the group consisting of silver chloride, silver chlorobromide and silver chlorobromoiodide and wherein said emulsion contains an alkylated polymer of a heterocyclic N-vinyl monomer of the lactam series in which the alkyl radical of said polymer contains from 2 to 2000 carbon atoms.

2. A light-sensitive silver halide emulsion according to claim 1, wherein said lactam polymer is present in amounts ranging from about 0.1 to about gms. per mole of silver halide.

3. A light-sensitive silver halide emulsion according to claim 1, wherein said emulsion is orthochromatically sensitized.

4. A light-sensitive silver halide emulsion according to claim 1, wherein said heterocyclic N-vinyl monomer comprises N-vinyl pyrrolidone.

5. A light-sensitive silver halide emulsion according to claim 1, wherein said alkylated polymer comprises a copolymer of a heterocyclic N-vinyl monomer and an a-olefin.

6. A light-sensitive silvenhalide emulsion according to claim 5, wherein said N-vin yl monomer comprises N-vinyl pyrrolidone.

7. A light-sensitive silver halide emulsion according to claim 6, wherein said alkyl radical contains 16 carbon atoms.

8. A light-sensitive photographic material comprising a base having coated thereupon a light-sensitive silver halide emulsion according to claim 1.

9. A process for treating a light-sensitive silver halide emulsion material which comprises developing an exposed silver halide emulsion in the presence of a stabilizer comprising an alkylated polymer of a heterocyclic N-vinyl monomer of the lactam series in which the alkyl radical of said polymer contains from 2 to 2000 carbon atoms.

References Cited UNITED STATES lPATENTS 3,043,697 7/1962 Forsgard 96l14XR 3,058,826 10/1962 Meerkamper et al. 96-114 XR 3,218,169 11/1965 Kelley et al. 96-114 3,252,801 5/1966 Cohen et al. 96-114 3,417,054 12/1968 Merijan et al. 260--66 3,423,367 1/ 1969 Merijan et al. 26066 RONALD H. SMITH, Primary Examiner U.S. Cl. XJR. 96--114 

